Jennifer Homans's history of the art, culture and political context of ballet is like a beautiful painting in a slightly askew frame. She is a former dancer who trained at the School of American Ballet in New York, and was the wife of the historian Tony Judt, who died in August. She exchanged the stage for academia two decades ago but one can still tell from her prose the kind of dancer that she was: meticulous, devoted and, au fond, profoundly romantic.

But her passionate identification with her subject leads Homans to a fatalistic conclusion. "For those of us who were there at the end of the last great era, and who experienced its vigour and its decline, the change has been momentous," she writes in her introduction and 550 pages later confesses that: "After years of trying to convince myself otherwise, I now feel sure that ballet is dying… we are watching ballet go."

Is this the measured judgment of a social historian or the lament of an American dancer for whom, as for many of her colleagues and compatriots, the lights went out in 1983 with the death of George Balanchine? She is both things at different times and she has strongly held opinions which, as in the case of her peremptory dismissal of Kenneth MacMillan, verge on the chauvinistic.

Ballet, she writes, "is an art of high ideals and self-control in which proportion and grace stand for an inner truth and elevated state of being". That such an art must redefine itself for an era as cynical and fragmented as our own is a truth that she acknowledges, but she has little patience for those attempting the task. Balanchine and Ashton make the cut, but MacMillan is dismissed pretty much out of hand.

By the end, Homans writes, MacMillan "had reduced ballet's eloquent language to a series of barely audible grunts". Such a reductive verdict is unworthy of a writer of her sophistication. Some of MacMillan's experiments failed, but others succeeded gloriously, and in damning him for attempting to take ballet into new territory while simultaneously bewailing the art form's incipient demise, she demonstrates only that she, not ballet, has run out of steam.

There has probably never been a time in the past 200 years when it was not at least half true to say that most choreography "veers aimlessly from unimaginative imitation to strident innovation"; one can imagine Théophile Gautier murmuring as much to Jules-Henri Vernoy de Saint-Georges in the foyer of the Paris Opéra in 1840.

If she takes a dim view of ballet's living practitioners, Homans writes with translucent beauty and authority of its lost past. She takes us back "to the religious and humanist origins of ballet: back to the Great Chain of Being, to angels and the harmony of spheres, to the court of Louis XIV and the strict aristocratic etiquette that had first given ballet its forms". From the Enlightenment and the story-ballet, she sweeps us to the late-1700s and the French Revolution. Here, at the Paris Opéra, was born the first modern corps de ballet, a group of maidens in white, the colour of revolutionary purity and virtue, whose role on stage was an essentially ethical one: to represent the community and the nation. Eventually, these maidens were "picked up and transformed in the imaginations of Romantic poets and writers and given canonical form in La Sylphide and Giselle".

Insights like this give Homans's history profound resonance and it's only rarely that her contextualising looks forced. Few would disagree that the 19th-century ballerina Marie Taglioni "fused the elegance and refinement of a lost aristocratic past with a new and airy spirituality", but to say that her dancing "seemed to echo a more general and pressing desire for reconciliation" in the wake of the Bourbon restoration is probably stretching a point.

The case that Homans makes wholly convincingly, in the case of Taglioni and others, is that the great dancers and choreographers of the 18th to the 20th centuries succeeded at least in part because of their ability to reproduce the "emotional tone" of the eras in which they lived. Her description of Balanchine's 1957 ballet Agon, arguably the most important dancework of the 20th century, is a tour de force, but she anchors it in hard fact. Originally danced by Arthur Mitchell, who was black, and the "pale and icily detached" Diana Adams, the ballet premiered "at a critical juncture of the civil rights movement… less than three months after the riots at Little Rock high school in Arkansas".

That she fails to bring the same macro-micro gaze on our own times, and has nothing to say about such choreographers as Alexei Ratmansky, William Forsythe or Wayne McGregor is a pity, for they reproduce, just as surely as the dead masters, the emotional tone of our own day. And any analysis of ballet which fails to mention China or Japan, almost certainly the seedbeds of the next classical dance-boom, is wilfully self-limiting.

But then almost everything that Homans the cool-eyed historian tells us refutes the conclusion of Homans the bereft dancer. For what she demonstrates is that ballet abides. That it marks time, it vamps until ready. And then, in scintillant and unexpected form, is reborn.